It is known that applying light of particular wavelengths (e.g., red or IR) to a human body part (e.g., a finger) and measuring the light transmitted through the body part can be used to detect blood flow (e.g., a pulse), components in the blood (such as hemoglobin), fat, and other characteristics. Generally, the light absorption correlates to particular characteristics.
However, such systems are generally limited to medical devices performing only a single function. Further, since the measurement of light absorption is through the body part, the device must be specifically made to surround the particular body part being tested, such as a finger.
What is needed is a more flexible and compact biologic sensor that can be used for a variety of functions and can be used for medical as well as non-medical purposes, such as authentication of the user. For user authentication, the biologic sensor should be able to be easily integrated into existing consumer products.
U.S. Pat. No. 9,570,002, in column 31, describes adding IR LED emitters into the matrix of a full color display screen along with photodetectors. The user may then touch the screen, and an image of the user's fingerprint may be detected by detecting the reflection off the ridges of the fingertip touching the screen. The detection is only of the surface of the fingertip and does not measure any light absorption at a depth into the finger, such as to detect a blood vessel or blood flow. Therefore, if the device is used for authentication, a simulated/forged fingerprint can fool the device. Additionally, the display screen is an array of closely packed red, green, and blue LEDs, and it is difficult to add IR LEDs and photodetectors into the existing array of LEDs without losing resolution. Further, it would be very expensive to develop a new display screen with integrated display pixels and detection pixels.